1. Field of Invention
The present invention relates to, in general, a combination of a power-supply control device and at least one light-control device equipped to operate at least one semiconductor light source and, in particular, such a combination on-board a motor vehicle.
2. Description of Related Art
A combination of this type is known per se, wherein the power-supply control device is equipped for supplying the lighting control with power via a supply line connected to a first connection pin of the power-supply control device and to monitor currents flowing through the connection pin of the power-supply control device and make use of diagnoses of the appliance connected to the respective connection pin.
A power-supply control device can be understood to be a power-distribution center in a motor vehicle and is designed to control appliances in the motor vehicle—such as, for example, a central locking system, a sunroof, and light sources of the motor vehicle—and monitor their functions.
Power-supply control devices are mass-produced articles, which should be capable of being implemented in the broadest range possible and, therefore, also fulfill their function in connection with appliances the properties of which differ from one to another. Examples of appliances having differing properties are to be found in light sources, which, for example, can be implemented in the form of incandescent lamps, gas-discharge lamps, or semiconductor light sources. Regardless of whether a motor vehicle is equipped with, for example, semiconductor light sources or with incandescent lamps, it should be possible in both cases to use the same power-supply control device.
Incandescent lamps such as halogen lamps and semiconductor light sources differ in the manner by which they are activated. Incandescent lamps such as halogen lamps are operated using a continuously flowing operating current of approx. 4-5 A. In contrast, for the operation of semiconductor light sources, such as those used in motor vehicles, a significantly lower operating current of, for example, 50-1.00 mA is sufficient. Furthermore, semiconductor light sources are frequently operated with a pulse-width-modulated current instead of a continuously flowing current.
Difficulties in the monitoring thereof occur from the specified differences in the activation of such lamps. The connection pins for conventional power-supply control devices each exhibits a high-side actuator (i.e., an actuator connected at an input end to a supply potential) equipped for connecting and/or disengaging an appliance lying at the output connection to or from a supply potential.
For the monitoring of the current flowing through the high-side actuator of a connection pin, the known power-supply control device exhibits, in particular, an ““open load” detection” function. In an “open load” state, no power flows through the high-end actuator, which may, for example, be the case with a defective appliance. To detect such a state, the power-supply control device checks whether the operating current flowing through a specific connection pin is less than a threshold value of, for example, 100 mA.
Because incandescent lamps such as halogen lamps are operated with a continuously flowing operating current of approx. 4-5 A, a threshold value of this type enables the power-supply control device to securely differentiate between defective and functioning incandescent lamps.
This does not, however, apply to semiconductor light sources because their normal operating current of, for example, 50-100 mA is already much closer to this threshold value. It is also problematic that semiconductor light sources are frequently operated with a pulse-width-modulated current instead of a continuously flowing current. For the pure control function, a pulse-width-modulated current of this type could consist of current breaks and phases of an amperage deviating from zero, wherein the amperage lies above the specified threshold value.
In the current break, the amperage may be equal to zero or so close to zero that it is at least less than the specified threshold value. When the power-supply control device then maps the pulse-width-modulated signal during a current break, the lower amperage of the current break could be easily interpreted as an error because low values of this type also occur, for example, during a power failure.
To prevent the power-supply control device from generating inaccurate error messages of this type, until now, it has been known to provide light-control devices equipped for the operation of semiconductor light sources coupled to the power-supply control device with amperages that are unnecessarily large for the operation of the semiconductor light sources. One has supplied light-control devices of this type by the power-supply control device with a current, for example, the amperage of which is so high (even during the current breaks of the “PWM” signal) that the power-monitoring function of the power-supply control device does not register any falling below of the threshold value.
A minimum amperage of this type lies, for example, at a value of 200 mA. As has already been mentioned, however, it is possible that only 50-100 mA are necessary for the operation of a semiconductor light source (in particular, a light-emitting diode). The excess power resulting from the difference occurring thereby is converted to heat by circuitry measures in the light-control device. In addition, the amperage not needed by the semiconductor light source during the current breaks is diverted to a supplementary load, such as an ohmic resistor, within the light-control device. Expressed heuristically, one has persuaded the power-supply control device that an incandescent lamp is being operated.
This approach has disadvantages in the form of an unnecessarily high power consumption. From the necessity of having to discharge larger quantities of heat as well, there is the additional disadvantage that numerous heat-sink volumes and surfaces are required than would be needed with a more energy-efficient system. The higher degree of energy efficiency provided by the semiconductor light source is, thereby, at least in part sacrificed.
With this background, an object of the invention consists of providing a combination of a power-supply control device and at least one light-control device of the type specified above that does not exhibit the disadvantages specified or exhibits them to a significantly reduced degree.